In this specification the term “light” will be used in the sense that it is used in optical systems to mean not just visible light, but also electromagnetic radiation having a wavelength outside that of the visible range.
Optical modulator and polarisation multiplexing devices are complex and typically have large form factors on lithium niobate (LiNbO3) substrates. Further, additional devices, such as variable optical attenuators (VOA) and photodetectors (PD), are often required to be included. The addition of such devices increases considerably the complexity and length of the overall multiplexor chip.
An increased chip length can be of significant importance in chip design because of limitations on maximum chip length due to a given wafer size—chip length must not exceed a given value in order to have a reasonable number of chips on each wafer. Moreover, the length of a package (which includes the modulator or multiplexor chip) is a significant parameter for placing the device inside a transponder or on a line card. Therefore, it is desirable to have a reduced optical modulator chip size.
It is possible to implement an optical modulator using discrete components. However, the package size is then considerably increased due to the required interconnections between the different components.